The terms warewasher and dishwasher may be used interchangeably herein. Further, the term commercial dishwasher (to which this invention is directed), is intended to distinguish from a "domestic" diswasher, the type commonly found in home use. Domestic and commercial dishwashers differ substantially in design and manner of use, with the possible exception of a few commercial machine styles which are an outgrowth of domestic unit designs. Even though these latter designs may appear similar in many respects, they differ in function and operation, not only in the length of time it takes to wash and rinse a rack of ware, but also in the number of washes and rinses per rack. Domestic units ordinarily have the further capability of drying washed dishes within the wash chamber, whereas comparable commercial units feature air drying outside the chamber in order to minimize the time it takes to complete each rack of ware. It is important in a commercial environment to wash racks successively in rapid order. Thus, a commercial washer is used for washing and rinsing but not for drying, because of the length of time it takes for the latter.
Domestic dishwashers may operate as long as 60 to 90 minutes to complete washing, rinsing and drying a single rack of dishes per day, whereas in a commercial establishment, a dishwasher will wash and rinse a rack of dishes in two to three minutes or less and require their immediate removal and replacement with the next rack. The cleansed ware is air dried in the racks, outside the dishwasher. It is rare in a domestic environment to wash consecutive racks or loads of dishes, whereas it is routine in the commercial environment, for example, where an operator may wash one rack after another of dishes during and after a lunch period at a restaurant. Most regular washing cycles of domestic machines include a substantial period for drying in the machine.
In the commercial environment racks of dishes or other ware are successively washed and rinsed in rapid fashion over a very short time cycle for each rack, typically in the order of two to three minutes. The kind of commercial dishwasher to which this invention is applicable is commonly referred to as a "stationary rack machine" i.e., a unit with an enclosable wash chamber in which a rack of dishes is placed, washed, rinsed, and then removed and replaced by a second rack of dishes, while the cleansed rack is air dried outside the chamber. There are two main types of stationary rack dishwashers, one type commonly referred to in the trade as a "fill-and-dump" (hereinafter "fill/dump") machine and a second type which has a large volume tank or reservoir, commonly called a "recirculating" machine, hereafter referred to as a "recirculating" or "tank" machine.
In a fill/dump machine, a single batch of water is typically used for each rack of dishes to be washed, in the following fashion. A sump in the wash chamber is filled with water, detergent added to make wash water, and a rack of soiled dishes placed in the chamber. The wash water is recirculated by a pump through a wash arm or arms having spray nozzles which spray the ware under relatively high pressure to loosen and remove the soil from the dishes. A drain valve is then opened to drain the sump of wash water by gravity into a waste line, usually located in the floor of the restaurant or cafeteria kitchen. The drain valve is then closed and a water line is opened to fill the emptied sump with fresh rinse water. This rinse water is then recirculated by the same pump and wash arm to rinse the ware. Upon completion of rinsing, the rack of rinsed dishes is removed from the chamber, but the rinse water is retained to serve as the wash water for the next rack of dishes, and detergent is typically added either automatically or by hand before the next rack of soiled ware is loaded into the machine.
Although the single batch of water is used as rinse water for one rack and then subsequently used as wash water for the next following rack, the end result (except for the first fill) is that one batch of water is used for each rack of dishes, but the filling and draining of water does not coincide with the beginning and end of a machine cycle. Examples of patents illustrating the type of dishwasher referred to herein are U.S. Pat. No. 4,088,145 issued May 9, 1978 to Tore H. Noren and U.S. Pat. No. 4,218,264 issued Aug. 19, 1980 to George J. Federighi and George B. Federighi. A variation of this type of unit illustrated in U.S. Pat. No. 3,903,909 issued Sept. 9, 1975 to Tore H. Noren and George J. Federighi, in which the batch of fresh water is introduced through the wash system to flush the wash system.
Although each of these patents shows a variety of different designs and functions, they essentially show the basics of a fill/dump machine, namely the recirculation of rinse water through the same instrumentalities that carried the wash water, and subsequently using the rinse water as wash water for the next rack of dishes. With such machines it is necessary to add enough rinse water to serve as the proper volume of wash water for a next rack of dishes. Such machines need to add enough rinse fill each cycle to satisfy the supply, without cavitation, of the pump which circulates the wash water and, in most designs, the rinse water as well. The amount is frequently stated as being at least 1.7 gallons (6.435 liters) of rinse water, but frequently exceeds 2 gallons (7.57 liters) and sometimes is as high as 3 gallons (11.355 liters) per rack.
Quite a different scheme is used in the "recirculating" or "tank" dishwasher. The tank is a relatively large reservoir which is originally filled with as much as sixteen gallons of water and enough detergent is supplied to provide the proper proportion of detergent-to-water for washing. This water or wash liquid is used over and over for washing successive racks with most of the same liquid. The liquid is somewhat diluted with fresh rinse water each cycle. A drain valve is located at the bottom of the tank. The valve is part of an open vertical standpipe which provides an overflow level near the top of the tank. A fresh water spray system rinses the rack of ware at the proper time in a cycle, after it has been washed by pumped recirculation of the large volume of wash water.
A primary purpose for using the tank system is to provide a significant volume of wash water on the dishes, even though that water is reused and tends to get heavily soiled if not watched. The water is typically heated by a heater, and acts as a heat sink to maintain water temperature. A fresh water dedicated rinse is supplied to perform rinsing while the wash recirculation pump is off. By "dedicated" is meant that the rinse system is used to carry only fresh water and not transport soiled wash water. The rinse water descends to the top of the pool of wash water, and a fairly large percentage of the rinse water may overflow through the standpipe and out to the drain. The tank itself is ordinarily drained only every few hours, at which time the water in the reservoir is usually fairly soiled. Strainers are provided to catch any large particles of food or other material washed from the dishes and keep them from reaching the sump wash liquid. Detergent is replenished as needed. To drain the tank, the standpipe is lifted, and in so doing the entire large volume reservoir is drained by gravity into a floor drain.
An example of the type of system described as a tank system is shown in U.S. Pat. No. 4,439,242 issued Mar. 27, 1984 to James P. Hadden. One advantage of the tank system over the fill/dump system is that as little as 1.2 to 1.4 gallons (4.542 to 5.299 liters) of rinse water needs to be used per rack. With the large volume of water available for pumped wash recirculation, rinse water added through the dedicated rinse system can be a minimum quantity required to do an effective rinsing job.
In addition to these primary types of washers, there exists fill/dump machines which utilize fresh water, dedicated rinse systems of a type similar to those used in tank machines. Such machines are completely drained of wash water by gravity directly to a floor drain, and, as will be shown, are incapable of providing the energy and water savings of this invention, without specific modifications to achieve the intended objectives. These fill/dump machines require similar volumes of water per rack as the previously discussed fill/dump machines, to satisfy wash pump needs.
In terms of water temperature, commercial dishwashers are available in what the trade refers to as low temperature and high temperature machines. This simply means that the rinse water temperature in a low temperature machine may be 130.degree.-140.degree. F. (54.degree. to 60.degree. C.) and include a sanitizing agent such as sodium hypochlorite (common household bleach), or, in the case of a high temperature machine, the rinse water has a minimum sanitizing temperature of 180.degree. F. (82.degree. C.) to meet public health standards in the United States. It should be understood the the invention disclosed and claimed herein is useful in either low temperature or high temperature machines if the objective of obtaining water and/or energy savings is achieved.